The instant invention relates to an apparatus for determining processing and mixing characteristics of a variety of materials, for example, thermoplastics, fiberglass, clays, asbestos, quartz-base materials, and wood-related materials. Such materials often exhibit strong abrasive properties and, as such, have presented problems of damage to the test apparatus as well as of removability of such materials from the test chamber after they have been mixed and cured.
Accordingly, a long-standing problem in the area of characteristic testing of materials of the above-mentioned categories has related to the recovery of samples which have been mixed under conditions intended to otherwise stimulate those encountered during actual production.
In any such stimulation, it is of course desirable that the sample not be substantially altered or affected during the process of its removal from the test chamber. Accordingly, a problem which has been associated with test sample apparatus for thermoplastic and other materials has related to the ease of removability of the sample. This problem is closely related to the problem of reproduceability of test results conducted upon such samples. Damage to a particular sample will result in alterations of its characteristic, therefore, creating problems of correlation between various test sample operations. Thus, it may be appreciated that efforts in securing adequate quality control over various extrusion and other plastic-forming processes have been encumbered by the tendency of such plastic (and other) materials to resist removal from the test chamber.
More particularly, a typical prior art mixer would consist of a mixing chamber in which counter-rotating rotors impact against granules of the test material, thus involving pressure against both the walls of the mixing chamber and within the physical structure of the test material. For example, see U.S. Pat. No. 3,800,597 (1974) to Paul entitled "Apparatus for Determining the Processing Characteristics of Plastic Type Materials."
Such mixers are usually thermal-liquid heated and consist of a bowl and backstand. The backstand is generally equipped with a plurality of gears which serve to drive the rotors as well as to regulate their rates of rotation.
After the test material is introduced into the mixer bowl, it is heated and mixed until fluxing occurs. This produces various shear processes which are a result of the physical and chemical effects of the conditions of heat and pressure which occur during the mixing.
The measuring objective of such testing is to monitor the time span during which the material possesses its lowest viscosity, that is, the period prior to cross-linking. The time span is of significance in the optimization of process-conditions during extrusion, injection molding, lamination and other procedures.
The construction of commonly available mixers requires that the rotors rotate sufficiently long until the cross-linking or setting of the thermoplastic material occurs; however, in this approach, the rotating force of the rotors will often mechanically impair or destroy the sample, often reducing it to powder form. Thus, all that is sometimes left to test is a pulverized sample. Further, even where such pulverization does not normally occur, a partial impairment of the thermo-set physical structure of the sample is often unavoidable in effectuating its removal from the mixer bowl and later in the cleansing of the bowl, rotors and backstand so that the apparatus can be reused in future tests.
On occasion, the material may cure or harden within the bowl to such an extent that its removal is impossible without forcibly hammering or chiseling the sample out. Obviously, such an approach not only impairs the physical characteristics of the sample, but also can cause substantial harm to the test apparatus which may be formed of stainless steel and/or other material sensitive to abrasion and injury. Accordingly, it may be appreciated that such a procedure for obtaining thermoplastic samples has become a major drawback in the perfection of various plastic and material-forming processes. Hence, it is to be appreciated that a problem has long existed with respect to test reproducability and correlation of test results. The present apparatus may be viewed as a solution to the above set forth long-standing problems.